1. Field of the Invention
The current invention relates to communications. More specifically, the present invention relates to a method and apparatus for automatically adjusting the amount of gain or loss in a communication system in which signals are relayed between a master system unit and a remote unit.
2. Description of the Related Art
Modem communications systems are an important part of our society today. One such communications system is a wireless cellular communication system. In wireless cellular communication systems, communications between users are conducted through one or more base stations. The term forward link is used to refer to communications from a base station to a subscriber station, and the term reverse link is used to refer to communications from a subscriber station to a base station. A subscriber station is the device that is used by an individual who subscribes to a communication provider for communication services. For example, a person who uses a conventional cellular telephone is a subscriber to the cellular telephone services provided by a cellular telephone service provider, such as Leap Wireless International Inc.
By transmitting information on a reverse link to a base station, a subscriber may communicate with people at other locations through any one of a number of communications systems, including conventional telephones, cellular telephones, or the Internet. The base station receives the information (voice or data) from the first subscriber station and routes the information to a Base Station Controller (BSC). The base station controller routes the information to a Mobile Switching Controller (MSC). The base station serving the subscriber stations sends the information back to the subscriber on the forward link.
As a subscriber station moves about a wireless cellular communication system, the quality of the forward and reverse links (and the capacity of the forward and reverse links to transmit data) will vary. In particular, a user of a subscriber station may move inside a building or enter an area in which signals are blocked, such as a tunnel or valley. When the user does so, the subscriber station may not be able to operate due to the low energy level in the signal that is available to and from the subscriber station.
One solution to this problem is to establish a relay station that can receive signals from a base station and relay (i.e., retransmit) those signals to the user""s subscriber station. However, in complex structures, such as buildings having several floors and corridors, a simple relay station is not effective. Accordingly, another approach is to place a master system unit at a location from which signals to and from a base station can be transmitted and received, respectively. Signals are then communicated over a wireline to a remote unit. The remote unit transmits information received from the base station via the master system unit to subscriber stations within an area into which signals transmitted directly from the base cannot easily be received. Likewise, the remote unit receives information from subscriber stations within the area. The remote unit then communicates the information received from the subscriber stations over wirelines to the master system station. The master system station communicates the information over the air to the base station.
One significant problem with such a configuration of master system units and remote units is that power control is an issue. That is, the amount of power that is transmitted to and from a base station must be controlled in order to ensure that system parameters are not violated. For example, there may be limits imposed by a governmental agency (such as the Federal Communications Commission in the United States) on the maximum amount of power that can be transmitted. Such limits may be inadvertently violated by a system that employs a master system unit and remote unit if the gain/loss between the master system unit and the remote unit changes due to temperature variations, aging effects, etc. For example, if the remote unit is transmitting at close to the maximum allowed power output level and the amount of loss in the system decreases (or alternatively the amount of gain increases), then the system may inadvertently exceed the maximum allowed power output level.
Further complicating this problem is the fact that in some systems, power is dynamically controlled to ensure that power is transmitted to the subscriber station at the most desirable level. Accordingly, when the amount of power that is received by the subscriber station is lower than desired, the subscriber station requests more power from the base station from which the signal originated. Likewise, if the amount of power received by the subscriber station is more than needed (or more than desired for any reason), then the subscriber station requests the base station to reduce the amount of power. It is essential to the proper operation of the system that the base station responds to such requests. It is essential for the response to be detected by the subscriber station (i.e., that the power be either increased or decreased as requested). Otherwise, the subscriber station will continue to request a change in the power transmitted by the base station until the base station output power is either maximized in the case of requests to increase power, or minimized in the case of requests to decrease power.
Accordingly, there is a need for a system that allows a master system unit and remote unit to be used in a manner that ensures that the power can be controlled in a desirable way.
A method and apparatus for compensating for loss or gain variations in signals transmitted between a remote unit and a master system unit of a communications system is disclosed.
In accordance with the disclosed method and apparatus, the amount of power in signals received by the master system unit is measured. The amount of power that is transmitted from the remote unit is also measured. The difference between the two measurements is calculated. This difference is then used to determine the amount of loss or gain between the signal that is received by the master system unit and the signal that is transmitted from the remote unit. Preferably, the measurements are made using a filter, such as an infinite impulse response (IIR) filter. However, it should understood that the xe2x80x9cfilterxe2x80x9d might be any method for getting an average value over time. Furthermore, in an alternative and less desirable embodiment, the values measured may be instantaneous values.
The use of such a filter prevents instantaneous differences that are not indicative of the average gain/loss of the signal being received from having too great an effect on the measurements. In addition, in some embodiments of the disclosed method and apparatus, the time at which measurements are made at the input to the master system unit is correlated with the time at which measurements are made at the output from the remote unit to ensure that the calculated difference between the input to the master system unit and the output from the remote unit are properly computed. By correlating the signals in this manner, differences in the power levels over time and the delay between the time a change occurs at the input to the master unit and the time the change is seen at the output from the remote unit can be taken into account.
The gain or loss is then monitored in order to provide a dynamic means by which to determine the relative amount of additional gain or loss that is needed in order to maintain calibration on the system (i.e., maintain a constant loss/gain between the signal received by the master system unit and the signal transmitted by the remote unit).